I found a wire at the back of the transmission that looked like it had been snipped, and it's the same size as the wire to one of the solenoids he left me with. Near it is a threaded socket that looks like where it could go, but I can't make it fit.

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1985 190D 2.2L 717.411 5-speed
1983 300D Euro OM617.950

I have a feeling this isn't the stock transmission, since it doesn't look like the photo from post #5. My theory is that the previous owner upgraded it when he added the turbo. Crawled underneath today and took some photos, couldn't see a part number...would love to know where this is located. Looked up the black solenoid I posted before, seems that I have either a 722.3 or 722.4 transmission.

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1985 190D 2.2L 717.411 5-speed
1983 300D Euro OM617.950